Electric furnace



UNITED STATES PATENT OFFICE. u

HABDLD G. WEI'DENTHAL, OF CLEVELAND, OHIO, ASSIGNOR, BY MESNEASSIGNMENTS, '10 WESTINGHOUSE ELECTRIC @c MANUFACTURING COMPANY, ACORPORATION OF' PENNSYLVANIA.

ELECTRIC FURNACE.

Speciication of Reissued Letters Patent. Reissued June 6l 1922.

Original No. 1,304,425, dated May 20, 1919, Serial No. 262,780, ledNovember 16, 1918. Application for To all whom t may concern Be it knownthat I, HAROLD G. WEIDEN- THAL, a citizen of the United States, residingat Cleveland, in the county of Cuyahoga and State of Ohio, have inventeda certain new and useful Improvement in Electric Furnaces, ofwhich thefollowing is a full, clear, and exact description, reference being hadto the accompanying drawings.

This invention relates to electric furnaces and resistance elementstherefor, and has for its object the provision of a new, improved, andsimplified type o`f furnace; the provision of an electric furnaceparticu( larly adapted for manufacture in small sizes as required bybrass and bronze founders, aluminum founders, and the like, although ofgreat value in larger sized installations; the provision of a furnacewherein the largest possible amount of the heat generated shall beuse-fully employed; the provision of a furnace so constructed as `topermit the easy replacement of resistance elements if and when required;the provision of a furnace equally applicable to direct or alternatingcurrent systems; the provision of a cheap, efficient and long-'livedresistance element which shall be capable of withstanding hightemperatures and oxidizing atmospheres; while further objects andadvantages of my said invention will become apparent as this descriptionproceeds.

In the drawings accompanying and forming a part of this application Ihave shown one embodiment of my said invention, although it will beunderstood that these drawings are illustrative merely and are notintended to be exhaustive of all the various constructions andarrangements which may be employed within the scope of my inventiveidea.. In these drawings Figure 1 is a vertical Sectional view of asimple type of furnace constructed in accordance with my invention,together with a simple mounting therefor; Fig. 2 is a top plan view ofsaid furnace a part of one side being broken away t0 show the internalconstruction; Fig. 3 is a view partly in elevation and partly in'longitudinal section, of my improved lresistance element, togetherwith-a preferred type of electric connection; and Fig. 4 is a top planview of the preferred connecting device.

Describing the parts by reference characters, 1 represents the shell ofmy improved reissue led March 25, 1920. Serial No. 368,685.

furnace which is preferably cylindrical in shapeJ and made of steel orother rigid conducting material of a considerable resistance to fusion.The same is provided with trunnlons 2-2whereby itmay either be held inan approxlmately upright 'position for use, rocked .for the purpose ofagitating the melt, or 1ncl1ned for purposes of pouring. The bottom ofthis shell is closed by a plate 3. The trunnions are here shown as'ournaled at the top of uprights 4-4 carried y a movable car or truck 5,although the method of mounting'the furnace may be varied widely withoutdeparting from the scope of my invention. The shell 1 is lined with therefractory material 6, and the bottom covered by refractory material 7,preferably in the form of bricks as shown.- Mounted upon the side wallsis a ring 10 of refractory material either molded or in block form asdesired, surrounded by a metal supporting band l1 and underlaid by ametal plate 12, the latter preferably having a downturned flange 13'loosely surrounding the shell 1 whereby it is heldin position. The roofof the furnace consists of refractory bricks 14 built inside the ring 10and suitably arched to carry the weight. This construction enables thetop part of the furnace to be' lifted oil as a whole in order to gainaccess to the furnace interior.

In the lower (part of the cavity thus defined there 'is locate -a moldedbath 15 of silica, magnesite, carborundum sand, or other suitable-refractory, the edge -of said bath being extended outwardly through theshell 1 at z one point as shown at 16 to forma pouring lip whoseextremity is supported by 'a metal nose 17 carried by the shell.Surrounding the bath 15, inside of the refractory walls 6 6 are locatedone or more arcuate conducting elements 20-20, here shown aselectrically connected to the botom plate 3 by means of metal plates21-21. It will be understood, however, that electrical connection can bemade in other ways but I prefer this construction as being the simplest.

The resistance elements are shown at 25-25 and are made in the formofelongated" y rods set in vertical position' around the interior of thefurnace walls with their lower yends resting on the conductors 20--20and the conductors -20 and embrace the elements rather closely, beingmade of suf` ficient thickness at this point to resist chipping oraccidental breakage.

The number, size, and arrangement of the resistor elements willvary,according to the use to which the furnace is to be put, the nature ofthe current employed, and the heat to be generated, but a space willordinarily be left at the pouring lip and also at one or more` otherplaces to permit the location of operating and inspection openings 27.In the present embodiment'I have shown the resistors as arranged inthree equidistantlydoors -27 spaced gangs, and have shown theconductors' 20 as consisting of three spaced seg"` ments, the same beingso located as togive space forthe pouring lip 16 and also for the ofwhich two are indicated. This is `the preferred yconstruction for usewith three phase current, the upper ends of the several gangs ofresistors being connected to suitable conductors 28 to which areattached y the current leads (not shown).. 4Either A connection or Yconnection can be employed, the neutral lead where used belng suitablyconnected to the conductors 20 in the present case through the shell ofthe furnace. v

In case double phase current be employed the resistors can be arrangedin twov equal banks, and in case `monophase,` alternating current ordirect current be em loyed the Same can be connected ,togetherinparallel as will be apparent to those skilled in the art, the conductors20.being similarly rearranged as may be necessary to make properconnection therewith. The conductors 20 can be made in continuouscircular form if v desired, but I prefer to make them of a discontinuousnature and to connect them electrically by metallic conductors, whetheror not those conductors be grounded upon the @shell as herein shown,since cracking and breaking of the same owin to unequal expansion isthereby reduce and its occurrence rendered less obnoxious. y Anysuitable or desired material can be emplo ed for these resistors, butlthe material which I prefer consists essentially of carborundum or theso-called carborundum sand which is the granular or amorphous materialproduced in large quanl tities in the manufacture of crystalline car-,borundum and consistin tially combined composition of. carbon and i ofcertain parsilicon. It is formed to the desired shape by being mixedwith a suitablebinder y such as molasses, tar, water glass, ory glue andbaked until the volatileconstituents of the binder are driven o'. Ipreferably coat the exf terior of each element with finely dividedcrystalline carborundum (which is easily accomplished by rolling theelement therein or sprinkling the same therewith prior `to baking),since the resistance of this material to atmospheric action at hightemperature is greater than that of the carborundum san Carborundum,either in they crystalline form or the amorphous and partially combinedform, possesses a very small electrical conductivity when cold, which,however, increases rapidly with rise of temperature until a red heat isreached, after which its change becomesV much smaller and more nearlyuniform. Accordingly, for the purpose of initiating the operation Ipreferably 4provide at least one resistance element of each gang `withya core of material which will conduct electricity with' the properfacility at ordinary'temperatures, trusting to the shielding effect ofthe carborundum to prevent the disintegration of the same at the highertemperatures under which the furnace is operated. This core may beeither of carbon-` or of some suitable metal or alloy. 'I

prefer to makethe same of nely divided carbon tamped inside alongitudinal bore with which the element is formed, since the initialresistance of such granular carbon is sufficiently high to enable theemployment of a core of considerable size and rapid heating effect',while the carborundum shell will prevent any1 serious oxidation at hightemperatures. owever such materials as the high resistance alloys ofiron and chromium, well known in the trade under the naine of nichromecan be employed, or many other alloys, or even iron wire .in someinstances, although such metallic conductors are necessarily of muchsmaller size and hence of slower heating elfect as well as being' moresubject to breakage in use. It is desirable that the resistance-of thecore be at least as high when cold as that of the carborundum part ofthe core v when hot, since otherwise it would require more current tostart the furnace than toy operate it; and in case a part of theelements are to be of plain construction, and onlya few of the coreformation, it is necessary that the combined resistance of the coreresistor when heated be approximately the same as that of the plainresistors iii order to secure uniform currentr distribution. Carbonfulfils the conditions more easily than any other substance with which Iam familiar, although other materials can be employed if suitable careis .used in the designing. l

Each of the resistance elements can, if desired, be made of thisinternally cored construction and such an` arrangement is frequentlydesirable as conducingto a more rapid starting of the furnace; but it issufficientfor practical purposes, at least where the resistance elementsare located 4closely together,to makeonly one element of each gang witha core, since the heating effect of neighbors vinto operation.

It'will be understood that in some cases i i the conductors can be madeas a part of the bath itself or the material to be heated can be soutilized; I have here shown the members 20, 20 as being Qf carbon,trustingto the shielding effect of the banks to protect them againstoxidation, but it will be understood that in some cases the entire bathor bosch can be made of carbon or of some metal, and thus be itselfconducting at all temperatures; or if made of a pyro-conducting materialsuch as magnesite or carborundumhit will become an additional conductorat high temperatures.

In case any element should be broken o destroyed the same can easily beremoved` and a new one substituted therefor without disturbing any otherpart of the furnace, and to facilitate this replacement the conductors28 ai'e preferably so arranged that the resistors are securedAindependently of each other; for example the same may be made in theform of an arcuate casting having therein a plurality of recesses 3()parallel to the axis thereof and provided at one side with gibs 31adapted to be clamped upon the resistors by means of set screws 32; andfor the purpose of conveying current to the conducting core of suchelements as have cores, over-hanging metallic arms 33 are provided(preferably upon the gibs since the saine are easily removable, althoughnot necessarily so located) and these arms are provided with Contactmembers 34 adapted to engage the conducting core, said contacts beingeither fixed or movable as may be desired, although I have shown thesame as consisting of a vertical set screw the better to provide forvariations in the length of the element or in the closeness of contact.It will `be clear that independent clamps can equally well be employedand the conductor made of other substance than metal.

Itwill be apparent that the resistors need notbe exactly upright but maybe considerably inclined if desired; that their number and arrangementmay be varied greatly; that the method and fittings for connecting themtogether and to the current source can be varied widely within myinvention; that the detail construction of and the method of, mountingthe furnace can be modified largely, and other changes made within thescope of my invention.

Having thus described my invention, what I claim is 1. In an electricfurnace, a refractory casing having uprightwalls, a refractory bath inthe lowery part of said casing, an arcuate conductor located betweensaid b ath and the casing wall, said conductor bein located entirelybeneath the bank of sai bath, a plurality of resist-ance elementsarranged in 'rior of said bath and the interior of the approximatelyupright position around the interior of said casing having their lowerends rest-ing on said conductor, and electrical connections to the upperends of said resistance elements.

2. In an electric furnace, a refractory bath having a basin shape,refractory walls rising above the banks of said bath, a roof connectingsaid walls at a distance above said bath, a refractory conductor locatedbetween said bath and the casing wall, a plurality of resistanceelements arranged around said refractory walls between said bath androof and having their lower ends resting on said conductor, andelectrical connections to thenpper ends of said resistance elements.

3. In an electric furnace, a refractory casing having substantiallyupright walls, a refractory bath in the lower part of said casing, aroof covering the upper end of said casing, a conductor located betweenthe exterior of said bath and the interior of the casing wall, said roofhaving an aperture above said conductor and close to the casing wall,anda resistance element having its lower end resting on the saidconductorand its upper end projecting through said aperture.

4.- In an electric furnace a refractory casing having a substantiallyupright cylindrical wall, a refractory bath in the lower part of saidcasing, a roof covering the upper end of said casing, a segmentalrefractory conductor located between the exterior of said bath and theinterior of the casing wall, the segments of said conductor beingsymmetrically spaced about said bath and said roof having a row ofapertures located above each segment of said conductor and 105 close tothe casing wall, a plurality of elongated resistance elements havingtheir lower ends resting on the said conductor and their upper endsprojecting throughl said apertures, and means outside of said furnacefor 110 connecting together the upper ends of each gang of elements.

5. In an electric furnace, a refractory casing having substantiallyupright walls and a roof connecting the same, said roof having 115 aseries of spaced apertures therein adjacent to the casing wall, arefractory bath in the lower part of said casing, a plurality ofsectional conductors located between the extecasing wall, meansconnecting said conductors electrically together, elongated resistanceelements resting on said conductors and projecting through saidapertures, and means above said' roof for connecting said 125 resistanceelements electrically together and to a source of current.

6. In an electricfurnace, a refractory casing, a refractory bath in saidcasing, a plurality of refractory conductors located inside the Wall ofsaid casing'and outside of and beneath the edge of said bath, aplurality of elongated resistors resting upon said conductorsandextending along" said casing wall above the edge of said bath, andmeans-for connecting theupper ends of said resistors to a source ofelectric current.

7. In an electric furnace, a bath,` conducting elements embracing saidbath, and a plurality of` independently removable resistance elements'arranged in upright position around Said bath With their lovver endsresting upon said conducting elements.

8. In an electric furnace, a bath, conduct-- ing elements embracing saidbath, a -plurality of independently removable resistanceelementsarranged in upright position around said bath With their lowerends resting upon said conducting elements, and other conductingelements engaging `and connectf ing together the upper ends of saidresistance elements.

9. In an electric furnace, a refractory bath, conducting elementsarranged outside of said bath and beneath the upper edge thereof, and aplurality of upright elongated resistance elements arranged around saidbath and making contact With said conductors. i

10. In an electric furnace, a refractory bath, conducting elementsarranged outside of said bathv andbeneath the upper edge thereof, aplurality `of gangs of upright elongated resistance elements arrangedaround said bath and making contact With said conductors, and otherconductors engaging and connecting together the upper ends of theLelements of each gang.

11. In an electric furnace, in combination, a pair of contact members, aplurality of resistors extending in parallel from one member to theother, certain of said resistors being composed entirely of a materialwhich is electrically conducting at elevated temperatures andelectrically resisting at ordinary temperatures, and others of the sameconsisting of a shell of such refractory material which is electricallyconducting at a high'temperature While being `substantiallynon-conducting at ordinary temperatures and having cores of materialwhich is conducting at ordinary temperatures, the combined resistance ofthe core and shell of said last named resistors being substantially thesame at `the working temperature as that of the plain resistor.`

12. In an electric furnace, a plurality of gangs of resistor elementsarranged around the Working cavity thereof, the resistors of each gangbeingy electrically connected in parallel, part of the resistors of eachgang being made of a refractory material 'which is electricallyconducting at high temperasistors of each gang consisting of a shell ofrefractory'material which is electrically, conducting at hightemperature While being substantially non-conducting at `ordinarytemperatures, and also having a core of material which is conducting atordinary temperatures, thel resistance of each of the last mentionedresistors rat the Working temperatures being substantially the same asthat of the resistance of the plane of the firstr mentioned resistor atWorking temperature.

13. A resistor element for electric furnaces consisting essentially ofcarborundum and having a core of material which is conductive 'atordinary temperatures and also infusible at the Working temperaturesofthe furnace, the resistance of said core when cold being at least asgreat as that of the carborundum at the Working temperature.

111. A resistor element for the purpose described consisting essentiallyof an elongated rod of carborundum sand held toether by `a binder andhaving an external ing essentially of an elongated `rod of carborundumsand held together by a suitable binder and having an external layer offinely divided crystalline carborundum, and the other consistingessentially of an elongated rod havingr acarbon core and an externallayer of finely divided crystalline carborundum, the size of said corebeing so chosen that the electrical resistance of said resistors isessentially equal at the Working temperature. 3

16. In an' electric furnace, a resistor consisting essentially of a`refractory substance Whichgis substantially a non-conductor at crdinarytemperaturesand al resistant conductor at high temperatures, saidresistor having ka core of resistance material which is electricallyconducting at ordinary temperatures, and terminal contacts for` saidresistor adapted to engage both said refractory and said core.

17. Inan electric furnace, a resistor consisting` essentially of arefractory substance which is substantially a non-conductor at ordinarytemperatures and a resistant conyrefractory part of said ,resistor andmaking electric contact therewith, and a part car- 'ried by saidterminal and electrically connected thereto but movable independentlythereof for makingycontact `with said core.

18. In, an electric furnace, the combinay tion with a bath andconducting elements embracing said bath, of a plurality of elonvresistoroperatively gated resistors arranged in gangs about said bath with theirlower ends contacting with sald conducting elements, other con- .ductingelements applied to and subtend- 19. In an electric furnace, thexcombina-V tion with a refractory casing, of a conductor of arcuate form1n said caslng, a refractory engaging sald conductor, and electricalannectionsfor said resistor.

elements.

21. Inan electric furnace, the combination with a refractor casinghaving substantially upright wal7 a refractory roof for said casing anda refractory bath in said casing, of conducting means located in saidcasing and adjacent said bath, said roof having anaperture above saidconductor, and a. resistance element having one end in operativeengagement with said conducting means and its other end projectingthrough said aperture.` Y 22. In an electric furnace, the combinationwith a refractory casing having substantially upright walls and a roofconnecting the same, said roof having a series of space aperturestherein adjacent to the casing wall, and a'refractory bath in saidcasing of a plurality of sectional conductors located adjacent to saidbath in said casing, electrical connecting means for said conductors,resistors .operatively conductors and projecting t rough sald apertures,and electrical connecting means for said resistors located above saidroof.

23. In an electric furnace, the combination. with a solidrefractoryresistor comprising an outer part and a core part, the

electrical-resistance characteristics of the two parts being different,of a terminal member for said resistor comprising a part operativelyengaging the outer part of said resistor and a second part operativelyengaging the core part of said resistor.

In testimony whereof, I 4have hereunto subscribed my 1920.

HAROLD G; WEIDENTHAL name this 1st day of March,

engaging said

